1. Field of the Invention
The present invention relates to an image processing apparatus capable of performing enlargement/reduction processing of an image while also performing halftone processing of the image by the dither method.
2. Description of the Related Art
As a conventional image processing apparatus, a printer such as an electrophotographic printer described in, for example, Japanese Patent Application KOKAI Publication No. 56-90375 is available. This printer forms a pseudo halftone image by the dither method which is used to improve the gradation characteristics of a halftone image. In the dither method, a halftone image is processed by a dither matrix, especially an 8.times.8 dot concentration type dither matrix. In this case, seven types of scanning apertures are prepared on a dot concentration type dither image. The sizes of these scanning apertures are: 2.times.2, 4.times.2, 2.times.4, 4.times.4, 8.times.4, 4.times.8, and 8.times.8.
In this printer, after an image is read, the number of white pixels in each of the seven types of scanning apertures is calculated, and the calculation result is multiplied by a coefficient for correcting the influence of the size of each scanning aperture. Thereafter, the densities in the respective scanning apertures are compared with each other to determine a scanning aperture to be used, thus obtaining a pseudo halftone image.
As described above, in the conventional printer, a pseudo halftone image is formed by the dither method. However, in processing a halftone image by the dither method, since processes for obtaining estimated densities in a plurality of scanning apertures are sequentially executed one by one by programs, the overall processing speed of the apparatus becomes inevitably low.